Wavelength division multiplexing is one way in which the information capacity, bandwidth, of an optical fiber can be substantially increased. This is accomplished by using several optical carriers within a narrow spectrum, typically around 1550 nm, which individually carry information in the optical fiber. In such systems, the information is encoded onto each carrier. The carriers are then combined through an optical multiplexer which then permits simultaneous transmission of all carriers into the optical fiber. At the receiving end, the optical signals are passed through an optical demultiplexer which subsequently routes the individual carriers to their appropriate channel. The present invention relates to the measurement of optical parameters for individual carriers in a wavelength division multiplexed fiber optic system. In such systems, measurement of optical parameters on a per carrier basis are critical as they provide vital information regarding both the heath of the optical networks over which such systems operate in addition to the performance of the system. Such information can then be used for diagnosis and repair or for performance optimization actions.
The optical information sought can usually be determined by the measurement of wavelength, power, and optical signal-to-noise ratio all measured on a per carrier basis. The measurement of such parameters must be accurate, have a wide range, and be performed in a timely manner so as to provide the necessary information in the shortest amount of time for the appropriate actions.
The conventional approach to analyzing the optical parameters of a spectrally dependent system is to use an optical spectrum analyzer. These systems are generally based on using an optical tool known as a monochromater. Monochromater based optical spectrum analyzers are typically slow, large in size for most embedded and field applications, and tend to drift with time, giving poor absolute accuracy. In fact, for most applications more than one instrument is typically used to obtain key optical parameters such as those described above.
Accordingly it would be advantageous to provide a ratiometric wavelength and power detection system that accurately provides wavelength, power, and signal-to-noise ratio measurements on a per carrier basis. Further, it would be advantageous if such a system could be provided in situ to provide these measurements so that the information could be monitored on a continual basis. Alternatively it would be advantageous if such a system could be used as a stand alone diagnostic tool.